The present invention relates to a multi-stage expansion/suction type of cryogenic refrigerating system, wherein the Bernoulli""s principle that as the flow velocity of a fluid in a tube increases, pressure exerted by the fluid in the tube decreases is applied to a refrigerating cycle system so that low temperature can be achieved in a refrigerating chamber of a refrigerator by lowering temperature and pressure of a refrigerant in multiple stages when the refrigerant flows from a high temperature side to a low temperature side.
More specifically, the present invention relates to a cryogenic refrigerating system, wherein a specific refrigeration effect thereof is increased only by one compressor in such a manner that a process of lowering pressure of a low-temperature side refrigerant by means of strong suction force in an evaporated refrigerant carrying tube generated when a liquid refrigerant is expanded and injected at a high velocity toward an inlet of a double tube is repeatedly performed in multiple stages, and thus, evaporation pressure of the refrigerant can be maintained below suction pressure of the compressor and its stability can be ensured even in case of continuous operation thereof.
Generally, ultra low temperature is needed for long-term preservation of tissue, cells or genes, a semiconductor fabricating process, an apparatus for inducing a superconductivity phenomenon, etc. Particularly, in case of biological materials such as cells, if they are kept at temperature of xe2x88x92130xc2x0 C. or less that corresponds to recrystallization temperature of ice, water contained therein is not crystallized but is in amorphous state. Thus, since it is not likely that a cell membrane is destructed, the term of preservation therefore can be greatly prolonged over 10 years. Although there are various technologies for achieving such ultra low temperature, a method using a vapor compression refrigeration cycle or liquid nitrogen is widely used. In order to achieve ultra low temperature of about xe2x88x92135xc2x0 C. to xe2x88x92150xc2x0 C., it is necessary to employ a multi-stage cascade refrigerating cycle having three stages or more, or to use the liquid nitrogen having liquefaction temperature of xe2x88x92196xc2x0 C. However, since the liquid nitrogen is used up only once, it is necessary to refill the liquid nitrogen for another use. Thus, its use is inconvenient and its operating cost is increased. On the other hand, in case of the multi-stage cascade refrigerating cycle, there is a problem in efficiently achieving the desired ultra low temperature. In addition, there is another problem in that an apparatus employing the multi-stage cascade refrigerating cycle is complex in its structure, and thus, failures of the apparatus frequently occur and its operating cost is also increased.
In consideration of these problems, there has been proposed a cryogenic refrigerator, which is disclosed in an article, entitled xe2x80x9cTemperature in Refrigerating Chamber of Compressor-type Refrigeratorxe2x80x9d in Nikkei Mechanical, No. 496 (Dec. 23, 1996), pp. 44-45, Japan. The cryogenic refrigerator employs a two-stage cascade mixed-refrigerant refrigeration circuit (i.e., a combination of a two-stage cascade refrigeration circuit and a mixed-refrigerant circuit) for achieving lower temperature in a low-temperature side refrigeration circuit by using a high-temperature side refrigeration circuit
In the two-stage cascade mixed-refrigerant refrigeration circuit, achievable temperature in a final evaporator is xe2x88x92155xc2x0 C., and temperature obtained in the refrigerating chamber is xe2x88x92152xc2x0 C. As schematically shown in FIG. 2, there are the two separate high- and low-temperature side refrigeration circuits which in turn are connected with each other through a cascade condenser. The cascade condenser serves as an evaporator for the high-temperature side refrigeration circuit and as a condenser for the low-temperature side refrigeration circuit. The high-temperature side refrigeration circuit is used for achievement of further lower temperature in the low-temperature side refrigeration circuit.
In particular, in order to achieve temperature of xe2x88x92100xc2x0 C. or less, the mixed-refrigerant refrigeration circuit was employed in the low temperature side. A typical refrigerant is a mixed-refrigerant comprised of seven kinds of refrigerants such as R412A having evaporation temperature of xe2x88x9240xc2x0 C. for the high temperature side, and R508 (mixture of R23 and R116) having evaporation temperature of xe2x88x9286xc2x0 C., R22 having evaporation temperature of xe2x88x9241xc2x0 C., and R14 having evaporation temperature of xe2x88x92128xc2x0 C. for the low temperature side. The mixed-refrigerant goes through the respective stages to achieve the low temperature.
However, in the two-stage cascade mixed-refrigerant refrigeration circuit, since two compressors are separately installed in the respective high- and low-temperature side refrigeration circuits, consumption of electric power is increased and the structure of the refrigeration cycle thereof is complicated. In addition, in order to maintain the temperature in the refrigerating chamber at xe2x88x92152xc2x0 C., it is necessary to continuously operate the refrigerator. However, it is difficult to operate continuously and stably the refrigerator since there is a problem in that residual oil which has been moved along with the refrigerant from the compressor to a low pressure side is not completely collected into the compressor to cause the lubricating oil to lack on sliding surfaces in the compressor and consequently a cylinder of the compressor to get scorched and stuck. Moreover, there are also problems in that suction pressure at low temperature is reduced and refrigeration performance is reduced.
An object of the present invention is to provide a refrigerating system which ensures reliability of the equipment thereof by maintaining stable performance even in case of continuous operation of the cryogenic refrigerating system.
Another object of the present invention is to provide a refrigerating system which improves life or reliability of the equipment thereof by ensuring the smooth operation of a compressor.
A further object of the present invention is to provide a refrigerating system which ensures external competitiveness of a product by enhancing the refrigeration efficiency thereof over 20% and stabilizing the operation thereof at ultra low temperature.
The above objects of the present invention can be achieved by a multi-stage expansion type of cryogenic refrigerating system, wherein a liquid refrigerant is expanded at an upper portion of an evaporated refrigerant carrying tube and is injected toward a downstream side with respect to a flow direction of evaporated refrigerant vapor in multiple stages so as to strongly draw refrigerant vapor in the evaporated refrigerant carrying tube and thus to lower evaporation pressure of the refrigerant below suction pressure of a compressor. Since the evaporated refrigerant vapor is strongly drawn and urged at a high velocity, flow velocity and pressure of the refrigerant vapor are increased and the suction pressure of the compressor is maintained over predetermined pressure. Accordingly, volumetric efficiency of the compressor can be improved and residual oil in a refrigeration circuit can be completely returned to the compressor. According to the present invention, it is possible to achieve final evaporation temperature of xe2x88x92160xc2x0 C. and temperature of a refrigerating chamber of xe2x88x92156xc2x0 C.
Further, the above objects of the present invention can be achieved by a multi-stage mixed-refrigerant system comprising a compressor for compressing a mixed-refrigerant; an oil separator for separating oil from the refrigerant compressed by the compressor, collecting the separated oil into the compressor, and then discharging the refrigerant; a condenser for cooling the high-temperature and high-pressure gaseous refrigerant discharged from the oil separator to liquefy the gaseous refrigerant; a heat exchanger which is installed on an evaporated refrigerant carrying tube for directing evaporated refrigerant vapor to the compressor in order to lower temperature of the condensed liquid refrigerant and in which the condensed high-temperature liquid refrigerant is caused to discharge heat therefrom to the evaporated low-temperature refrigerant vapor and to be supercooled, and the refrigerant flowed toward an inlet of the compressor is heated and evaporated; a gas/liquid separator for separating the condensed mixed-refrigerant passing through the heat exchanger into the liquid refrigerant and the gaseous refrigerant; a plurality of expansion/suction apparatuses; and a final evaporator.
In the expansion/suction apparatus, the liquid refrigerant separated by the gas/liquid separator sequentially passes through an expansion device installed in a tube, is injected from a nozzle provided on an end of the tube toward an outer tube for the evaporated refrigerant of a double tube, is evaporated while flowing from an upstream side to the downstream side, and communicates with an evaporated refrigerant carrying tube on a high-temperature side. At this time, a throttling phenomenon occurs in the vicinity of the nozzle and the refrigerant vapor in the evaporated refrigerant carrying tube is strongly drawn, so that the drawn refrigerant vapor is caused to flow into the outer tube of the double tube from the upstream side to the downstream side along with the injected refrigerant which has passed through the expansion device. At the same time, the residual oil contained in the refrigerant is moved toward the compressor, and an inner tube for the condensed refrigerant disposed inwardly from the outer tube for the evaporated refrigerant of the double tube which has two concentric tubes of different diameters directs the gaseous refrigerant separated by the gas/liquid separator in an upward direction, so that the gaseous refrigerant is condensed and the condensed refrigerant flows into a gas/liquid separator on the low temperature side. In such way, the liquid refrigerant from the gas/liquid separator passes through the expansion device and is injected from the nozzle, and then, the injected refrigerant is caused to flow together with the refrigerant vapor drawn due to the injection of the liquid refrigerant, toward the high temperature side along an evaporated refrigerant carrying tube on the high temperature side which communicates with the double tube. The gaseous refrigerant from the gas/liquid separator is condensed while flowing upwardly through the inner tube for the condensed refrigerant of the double tube, and then flows into the gas/liquid separator on the low temperature side. In such way, the expansion/suction apparatus constructs one cycle. The plurality of expansion/suction apparatuses are connected with each other in multiple stages so that the expansion and condensation of the refrigerant are repeated, thereby sequentially achieving low temperature.
In the final evaporator, condensed refrigerant which has passed through a final expansion/suction apparatus is condensed again in a heat exchanger disposed below the final evaporator, and flows into the final evaporator through an expansion device. The refrigerant introduced into the final evaporator is evaporated while flowing downwardly. The completely evaporated refrigerant flows into an evaporated refrigerant carrying tube of the final expansion/suction apparatus. Therefore, an integrated circuit is formed.